John Stivers – Work Energy Power

Transcript:

When I looked at energy-101, I was amazed at how sophisticated some of the discussions were and it struck me that having a primer where I looked at WORK and ENERGY and POWER again might just be the ticket.

Well let’s start with work. Physicists define work as a force applied over a distance. If you take an object, say a toolbox and apply a force, 22 pounds of force and you move it two feet, you’ve done 44 foot pounds of work. In metric those units convert to 100 newtons of force, and let’s say we moved it 0.60 of a meter. So we’ve done 60 newton-meters of work. In the metric system that’s referred to as a joule, 1 newton-meter is 1 joule.

Again, work is a force acting over a distance and energy is the capacity to do that work. Or another way to look at it, in a perfect world, the amount of work done is equal to the amount of energy expended. As it turns out work and energy are measured in the same units. And in the metric system that’s a joule.

Energy as it turns out is an inherent property of any object. It’s the stored capacity to do work. When it comes to electrical energy the battery is a great example. There are other forms of energy generally connected with producing heat, like a chord of wood, a ton of coal, maybe a gallon of gasoline or our sun. We’ve got energy and work down now lets see how power relates to them.

Power is the rate at which work is performed so let’s take a look at that toolbox again. If we put a stopwatch to it and we do 60 joules of work in 3 seconds and divide it, we’ve done 20 joules per second that’s the rate at which power has been applied in order to accomplish that work. The basic unit of power, joules per second is a watt and the power that was applied to accomplish that work turns out to be 20 watts.

Watts are pretty common units of measure it’s what we use when we buy a light bulb, we see it on our toasters, or it was that 20 watts that I used to move that toolbox.

Many hands make for light work. Or another way to say that is the power that’s supplied the less work each individual device ends up doing or the quicker the work gets done. Power is also the rate at which stored energy gets converted. For example, you are driving along and you want to get around that slow car in front of you. You push the peddle to the metal. In essence what you are doing is increasing the amount of power that the engine delivers to the wheels and also you are converting the stored energy of the gasoline at a lot faster rate.

So to recap. Work is a force applied across a distance also, that relates to the energy consumed in accomplishing that work and they are measured in the same units. Power is the rate at which that work is produced or the rate at which we expend energy to accomplish it. This interrelationship between WORK and ENERGY and POWER are things once you are aware of it we see all the time in everything we do.